1. Field of the Invention
This invention relates to a semiconductor integrated circuit device and more particularly to a semiconductor integrated circuit device having dummy word lines.
2. Description of the Related Art
A dummy word line is used to drive a timing dummy bit cell and create a control signal which controls data reading timing, for example. Since it is required for the dummy word line to behave in the same manner as the normal word line, it is desirable to lay out the dummy word lines like the word lines. As a known reference which discloses the dummy word line, for example, U.S. Pat. No. 5,999,482 is provided.
Unlike the normal word line, since the dummy word line is driven each time the semiconductor memory is accessed, the frequency of application of voltage to the dummy word line is extremely larger in comparison with the frequency of application of voltage to the normal word line. Therefore, the possibility that a line breaking accident occurs due to electromigration becomes stronger in comparison with the case of the normal word line and will function as one factor which controls the service life of the device.